Lysosomal alkalinization, lipid oxidation, and reduced phagosome clearance triggered by activation of the P2X7 receptor.

Lysosomal enzymes function optimally at low pH; as accumulation of waste material contributes to cell aging and disease, dysregulation of lysosomal pH may represent an early step in several pathologies. Here, we demonstrate that stimulation of the P2X7 receptor (P2X7R) for ATP alkalinizes lysosomes in cultured human retinal pigmented epithelial (RPE) cells and impairs lysosomal function. P2X7R stimulation did not kill RPE cells but alkalinized lysosomes by 0.3 U. Receptor stimulation also elevated cytoplasmic Ca(2+); Ca(2+) influx was necessary but not sufficient for lysosomal alkalinization. P2X7R stimulation decreased access to the active site of cathepsin D. Interestingly, lysosomal alkalinization was accompanied by a rise in lipid oxidation that was prevented by P2X7R antagonism. Likewise, the autofluorescence of phagocytosed photoreceptor outer segments increased by lysosomal alkalinization was restored 73% by a P2X7R antagonist. Together, this suggests that endogenous autostimulation of the P2X7R may oxidize lipids and impede clearance. The P2X7R was expressed on apical and basolateral membranes of mouse RPE; mRNA expression of P2X7R and extracellular ATP marker NTPDase1 was raised in RPE tissue from the ABCA4(-/-) mouse model of Stargardt's retinal degeneration. In summary, P2X7R stimulation raises lysosomal pH and impedes lysosomal function, suggesting a possible role for overstimulation in diseases of accumulation.

Stimulation of the D5 dopamine receptor acidifies the lysosomal pH of retinal pigmented epithelial cells and decreases accumulation of autofluorescent photoreceptor debris.

Optimal neuronal activity requires that supporting cells provide both efficient nutrient delivery and waste disposal. The incomplete processing of engulfed waste by their lysosomes can lead to accumulation of residual material and compromise their support of neurons. As most degradative lysosomal enzymes function best at an acidic pH, lysosomal alkalinization can impede enzyme activity and increase lipofuscin accumulation. We hypothesize that treatment to reacidify compromised lysosomes can enhance degradation. Here, we demonstrate that degradation of ingested photoreceptor outer segments by retinal pigmented epithelial cells is increased by stimulation of D5 dopamine receptors. D1/D5 receptor agonists reacidified lysosomes in cells alkalinized by chloroquine or tamoxifen, with acidification dependent on protein kinase A. Knockdown with siRNA confirmed acidification was mediated by the D5 receptor. Exposure of cells to outer segments increased lipofuscin-like autofluorescence, but SKF 81297 reduced autofluorescence. Likewise, SKF 81297 increased the activity of lysosomal protease cathepsin D in situ. D5DR stimulation also acidified lysosomes of retinal pigmented epithelial cells from elderly ABCA4(-/-) mice, a model of recessive Stargardt's retinal degeneration. In conclusion, D5 receptor stimulation lowers compromised lysosomal pH, enhancing degradation. The reduced accumulation of lipofuscin-like autofluorescence implies the D5 receptor stimulation may enable cells to better support adjacent neurons.

The association between femoral neck shaft angle and degenerative disease of the hip in a cadaveric model.

BACKGROUND: While the influences of acetabular dysplasia and overcoverage on hip arthritis have been studied, the impact of femoral neck-shaft angle on hip arthritis is much more poorly understood. The purpose of this study is to determine if a relationship exists between neck shaft angle and the development of osteoarthritis, a better understanding of which would be useful to surgeons planning osteotomies about the hip. METHODS: 533 cadaveric femora and acetabulae (1066 total) from the Hamann-Todd Osteological Collection (Cleveland, OH) were acquired. We measured true neck shaft angle using an AP photograph with the femoral neck parallel to the table. Femoral head volume to acetabular volume ratio, representing femoral head coverage, as well as femoral version were utilised. Correlation between neck shaft angle, femoral version, femoral head coverage and osteoarthritis were evaluated with multiple regression analysis. RESULTS: The mean age and standard deviation was 56 ± 10 years. There were 64 females (12%) and 469 males. There were 380 Caucasians (71%) and 153 African-Americans. Mean femoral version was 11° ± 12° and mean true neck shaft angle was 127.7° ± 5.9° There was a strong correlation between age and arthritis (standardised beta 0.488, p < 0.001). There was a significant correlation between increasing true neck shaft angle and decreasing hip arthritis (standardised beta -0.024, p = 0.038). In the femoral head overcoverage subset, increasing true neck shaft angle was still significantly associated with decreasing hip arthritis (standardised beta -0.088, p = 0.018), although this relationship was not significant with femoral head undercoverage subset. CONCLUSIONS: With sufficient acetabular coverage, a relative increase in femoral neck shaft angle within the physiologic range is associated with decreased hip osteoarthritis. CLINICAL RELEVANCE: An understanding of the relationship between femoral neck shaft angle and hip osteoarthritis could be useful for surgeons planning pelvic or proximal femur osteotomies in children.

A Comparison of 30-Day Perioperative Complications for Open Operative Care of Distal Upper-Extremity Fractures Treated by Orthopedic Versus Plastic Surgeons: A Study of the National Surgical Quality Improvement (NSQIP) Database.

Purpose: To determine whether surgeon specialty affects complications after open operative care of distal upper-extremity fractures. Methods: We performed a retrospective cross-sectional study using the American College of Surgeons National Surgical Quality Improvement Database from 2005 to 2016. Patients were included if they received open operative treatment by an orthopedic or a plastic surgeon for distal radius/ulna, carpal, metacarpal, or phalangeal fracture. Univariate analysis and multivariable analysis of perioperative complications were performed to identify differences between the 2 specialties. Major complications assessed were 30-day reoperation and mortality. We also assessed transfusion, thromboembolic, surgical site infections, cardiac, pulmonary, and renal complications. Results: A total of 20,512 patients were included. Most cases performed by orthopedic surgeons (71.2%) were for distal radius/ulna fractures, whereas the majority of cases performed by plastic surgeons were for metacarpal (41.0%) and phalangeal (37.9%) fractures. No difference was identified in most perioperative complications between specialties. Plastic surgeons had a higher incidence of surgical site infections (1.2% vs 0.5%) on univariate analysis. However, when controlling for variables such as patient demographics and comorbidities in multivariable analysis, surgical specialty was not significantly associated with surgical site infection. Rather, surgery on phalangeal bones (adjusted odds ratio [aOR] = 2.745; 95% confidence interval [CI], 1.559-4.833), higher wound class (wound class 3 aOR = 3.630; 95% CI, 2.003-6.577), and smoking (aOR = 1.970; 95% CI, 1.279-3.032) were independent risk factors for surgical site infection. Plastic surgeons were found to operate on proportionally more smokers, patients with higher wound class, and phalangeal fractures (37.9% of all fracture cases) compared with orthopedic surgeons. Conclusions: Orthopedic and plastic surgeons achieve equivalent outcomes from a safety perspective after open operative treatment of upper-extremity fractures in terms of mortality and 30-day reoperation, which suggests that both specialties can safely perform call-related operative upper-extremity fracture care. Plastic surgeons operated on more smokers, patients with higher wound class, and phalangeal fractures, all of which were associated with increased incidence of surgical site infection, revealing differences in practice composition from their orthopedic colleagues. Type of study/level of evidence: Therapeutic III.

Six-Week Interval Between Preoperative Radiation and Surgery Is Associated With Fewer Major Wound Complications in Soft Tissue Sarcoma.

OBJECTIVES: A total of 30% to 40% of soft tissue sarcoma (STS) patients develop major wound complications (MWCs) after preoperative radiation (preRT). The optimal preRT-surgery interval and its association with MWCs is unknown. This study investigated whether a longer preRT-surgery interval is associated with fewer MWCs compared with historical controls. METHODS: All patients treated by a single surgeon after preRT with limb-sparing wide resection for extremity and trunk STS were retrospectively reviewed from 2004 to 2014. The primary outcome was MWCs defined as a secondary operation, invasive procedure, wound packing, or readmission for wound care. Secondary outcomes of local recurrence and survival were followed and independent variables were analyzed for an association with MWCs. RESULTS: Fifty-four patients were included with a median follow-up of 32 months and age of 61 years. The majority of tumors were deep (91%), large (median size of 11 cm), high grade (78%) and within the lower extremity (78%). The median preRT-surgery interval was 43 days and 80% of patients received surgery 35 to 49 days after radiation. MWCs were observed in 15% of patients and 88% occurred within 40 days. Predictors for MWCs on multivariate analysis were peripheral vascular disease (P=0.03), location in the medial compartment of the thigh (P=0.03), and neurovascular involvement (P=0.03). CONCLUSIONS: This study presents a cohort of STS patients with an extended preRT-surgery interval of ~6 weeks. MWCs in this population occurred at a lower rate than historical controls. Overall these findings support the exploration of a longer interval to reduce MWCs and their associated morbidity.

Pulley Release and Reconstruction With Acellular Dermal Matrix After Zone 2 Flexor Tendon Injury.

Zone 2 flexor tendon repair has been historically associated with poor outcomes, mainly due to stiffness. In an effort to minimize adhesions, accommodate flexor digitorum profundus and flexor digitorum superficialis bulk, and prevent bowstringing, we have developed a novel approach to flexor tendon repair that relies on aggressive flexor tendon pulley release and pulley reconstruction with acellular dermal matrix. This technique leverages the antiadhesive properties and high tensile strength of acellular dermal matrix to maximize gliding and prevent bowstringing. Here we describe the details of our technique and illustrate a case where this technique was employed.

Scaphoid Fracture Repair Does Not Significantly Diminish Short-Term Participation in the National Football League.

BACKGROUND: Fixation of scaphoid fractures is recommended in elite athletes to hasten healing and return-to-sport times. Complications such as nonunion negatively affect athletic performance. QUESTIONS/PURPOSES: The purpose of this study was to examine the prevalence and impact of scaphoid repair on National Football League (NFL) participation during athletes' first season in the NFL, while identifying significant predictors for development of carpal arthritis and scaphoid nonunion. METHODS: A total of 1311 football athletes invited to the NFL Scouting Combine from 2012 to 2015 were evaluated for history of scaphoid fracture repair. Athlete demographics, surgical history, and imaging and physical examination findings were recorded. Future NFL participation based on draft status, games played, and games started during athletes' first season were gathered using publicly available databases. RESULTS: Nineteen (1.4%) athletes underwent 24 operations for scaphoid repair. Limitations in wrist range of motion or strength were present in 47.4% of athletes with a history of repair. Arthritic changes were present in 32% of wrists, while radiographic nonunion was present in two athletes following scaphoid fracture. Defensive backs were observed to have a higher incidence for arthritic changes following repair compared to other positions. No significant difference in prospective NFL participation was found in athletes with a history of scaphoid repair than in those without. CONCLUSIONS: Athletes with a history of scaphoid repair are not at significant risk for diminished participation during their first season in the NFL.

Hip morphology predicts posterior hip impingement in a cadaveric model.

INTRODUCTION: Posterior hip impingement is a recently-identified cause of hip pain. The purpose of this study is to characterise posterior femoroacetabular and ischiofemoral impingement and identify its predisposing morphologic traits. METHODS: Two hundred and six cadaveric hips were randomly selected and taken through controlled motion in two pure axes associated with posterior hip impingement: external rotation (through the mechanical axis) and adduction (coronal plane). The range of motion and location of impingement was noted for each specimen. Morphologic traits including femoral/acetabular version, and true neck-shaft angle (TNSA) were also measured. RESULTS: External rotation impingement occurred between the femoral neck and acetabulum in 83.0% of hips, and between the lesser trochanter and ischial tuberosity in 17.0%. Adduction impingement occurred between the lesser trochanter and ischial tuberosity in 78.6% of hips, and between the femoral neck and acetabulum in 21.4%. Multiple regression revealed that increased femoral/acetabular version predicted earlier external rotation and adduction impingement. Unstandardised betas ranging from -0.39 to -0.64 reflect that each degree of increased femoral/acetabular version individually accounts for a loss of external rotation or adduction of approximately half a degree before impingement ( p < 0.001 for each). Increased TNSA was associated with earlier adduction impingement only (unstandardised beta -0.35, p = 0.005). DISCUSSION: Relative femoral/acetabular anteversion was associated with earlier posterior hip impingement. Coxa valga was associated with earlier adduction impingement, but protective against external rotation impingement. These findings highlight the importance of monitoring correction during femoral/acetabular osteotomies, as overcorrection of retroversion may predispose to earlier posterior impingement.

Prevalence of Jones Fracture Repair and Impact on Short-Term NFL Participation.

BACKGROUND: Elite American football athletes are at high risk for Jones fractures. Fixation is recommended to minimize nonunion and allow early return to play. The purpose of this investigation was to evaluate the prevalence of Jones fracture repair in athletes invited to the National Football League (NFL) Combine and the impact of fracture repair on short-term NFL participation compared to athletes with no history of repair. METHODS: A total of 1311 athletes participating in the Combine from 2012 to 2015 were evaluated. Athletes with history of Jones fracture repair were identified. Athlete demographic information was collected while physical examination findings were recorded. Radiographs were evaluated to determine fixation type and the presence of nonunion. Future participation in the NFL was evaluated based on draft status, games played, and games started in the athlete's first season following the Combine. RESULTS: Fixation was performed for 41 Jones fractures in 40 athletes (3.1%). The highest prevalence was in defensive linemen (n = 10 athletes), with the greatest rate in tight ends (5.1%, n = 4 of 79 athletes). Intramedullary screw fixation was used for all fractures. Incomplete bony union was present in 3 (8%) fractures. Athletes with a history of repair were not at significant risk for going undrafted ( P = .61), playing ( P = .23), or starting ( P = .76) fewer NFL games compared to athletes with no history of repair during athletes' first NFL season. CONCLUSION: Athletes with a history of Jones fracture repair were not at significant risk of going undrafted or for diminished participation during their first season in the NFL. LEVEL OF EVIDENCE: Level IV, case series.